1. Field of the Invention
The present invention relates to electronic musical instruments, and more particularly to electronic synthesizers.
2. The Prior Art
Electronic synthesizers have been developed in a variety of configurations. Practically all of the heretofore developed configurations employ some apparatus for generating an a.c. signal in response to operation of a manual control, such as a key of a keyboard or the like. Most configurations also include apparatus for varying the wave shape of the envelope used for modulating the amplitude or other characteristics of the output signal and means for passing the modulated signal through an audio amplifier system to a loudspeaker or the like. Signals are also sometimes passed through a filter having an adjustable bandpass, which modifies the characteristics of the sounds produced.
Previous designs for variable parameter filters required the use of relatively low signal levels and, as a result, are characterized by relatively low signal-to-noise ratios, which seriously limits the dynamic range of the instrument using such filters.
Accordingly, there is a need for a method and apparatus for controlling the frequency characteristics of a filter which is capable of a wider dynamic range than has heretofore been available.